1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to a power transmission belt with a light-colored, exposed, outer surface in which color bleeding, that might occur during the vulcanization process and deteriorate the appearance of the outer surface, is prevented. The invention also contemplates a method of forming such a belt.
2. Background Art
It is common to construct power transmission belts with rubber having carbon black as one of its components for purposes of increasing belt durability. The result of this is that most power transmission belts are black in color. In some environments, as for purposes of aesthetics, it may be desirable to have belts that are other than black in color. For example, belts used in the home, such as those on sewing machines, washing machines, etc., may be more desirably matched in color to the appliance on which they are used. This often requires the use of white and other light-colored belts.
Heretofore, belt designers have generally compromised either the performance of the light-colored belts or the appearance thereof. The competing objectives of appearance and performance are affected by different characteristics of the light- and black-colored rubber. The dark-colored rubber, with carbon black, exhibits excellent durability. On the other hand, light-colored rubber, while aesthetically pleasing, does not contain carbon black and is resultingly less durable than the rubber with carbon black. Consequently, designers of power transmission belts must arrive at a balance between aesthetics and performance.
The problem of arriving at this balance is aggravated by the conventional belt manufacturing process. That is, the belt components are normally put in place and subjected to high temperatures and pressures during vulcanization. The black rubber, laden with carbon black on the inside of the belt, tends to bleed out into the light-colored rubber during vulcanization and thereby deteriorates the appearance thereof. Typically, an outer cover canvas is impregnated with the light- colored rubber. The black rubber readily migrates through the canvas between the fibers thereof to be visible externally of the belt.
One solution to the above problem is to either thicken the impregnating of light-colored rubber on the canvas or to make the entire belt from light-colored rubber. In either event, an abundance of light-colored rubber tends to diminish belt performance.